This invention relates to a current divider circuit for receiving at a node a signal current and dividing the signal current in predetermined proportions between a plurality of current paths. The term signal current as used herein refers to any current whose purpose includes conveying information of some sort, in contradistinction, for example, to a mere supply current.
Current divider circuits as set forth in the opening paragraph are well known and are commonly used for generating scaled replicas of a reference current or other signal current in accordance with a desired weighting pattern. For example, in a digital-to-analog converter, several binary-weighted reference currents may be generated from a single master reference current. In the known circuits, each path usually comprises a transistor and the transistors of all the paths are designed to be identical or `similar`, meaning that the currents flowing through the different transistors are equal or are related in accordance with ratios defined by the relative geometries of the transistors. For example, the transistors may be bipolar (or MOS) types, with the emitter (or source) of each transistor connected to the input node and the base (or gate) of each transistor being connected to a common bias point. These circuits operate according to the well-known `current-mirror` principle where each current path has a similar impedance.
A problem arises, however, when it is required to pass a predetermined portion of the current at the node through a current path which has an impedance dissimilar to those of the other paths, because in that case the current mirror principle will no longer operate to define the relative proportions of current flowing in the current paths except as between the paths of similar impedance.